Generic switchable slot valves for coating plants are known. Valves of this type display a valve bore, aligned in a valve extent direction, which is in a valve main body and into which a supply duct opens and from which a nozzle duct leads out to connect to a slot nozzle of the coating plant. Disposed in the valve bore of a known slot valve is a valve control rod mounted in the valve bore to be rotatable about a rotation axis which extends in the valve extent direction and is penetrated by a valve duct which disposes of a duct inlet extending axially along an outer side of the valve control rod and a suchlike opposite duct outlet, the former and latter being interconnected by a valve duct which penetrates the valve control rod.
In those known slot valves, the valve control rod can be rotated between a throughput position and a closed position by a motor. In the throughput position, the valve control rod is disposed such that the coating material supplied through the supply duct can make its way through the duct inlet into the valve duct and from there through the duct outlet into the nozzle duct, from where it is supplied according to the intended use to the slot nozzle of the coating plant. In contrast, in the closed position, the nozzle duct is isolated from the supply duct by the valve control rod such that the deployment of coating material is interrupted.
To mount the valve control rod in the valve bore, the valve control rod on its outer side displays bearing faces which, for mounting in the region of two part-circumferences of the valve control rod, between the duct inlet and the duct outlet, bear on the circumferential face of the valve bore. Since the valve control rod is rotatable, there remains in the bearing region a bearing gap of at maximum 100 μm between the bearing faces and the inner circumferential face of the valve bore.
Generic slot valves control in a targeted manner delivery of the coating material through a slot nozzle. For this purpose, they are upstream of the slot nozzle and by rotation of the valve control rod enable temporary interruption of the supply of the coating material to the slot nozzle. This is particularly used to deliver coating material through the slot nozzle and interrupt delivery in an alternating manner.
Generic coating plants having generic slot valves are used in the manufacture of batteries, in particular. In this context, they deploy a pasty coating material which, in particular, contains electrochemically active particles such as graphite particles, for example, in the form of a thin layer. In particular, the layer may be applied as an electrode layer immediately onto a suitable collector of the battery. However, a coating is also understood to be the temporary application onto a carrier substrate such as a roller or a planar carrier substrate, for example, from which according to the intended use the layer formed by the coating material is removed again in later production steps, for example, for application onto a collector strip.
Apart from deployment of a coating material having electrochemically effective particles for the manufacture of a battery, coating plants of that type may also be used to manufacture an electrocatalytic layer of a fuel cell. In that case, in particular coating materials which contain catalyst particles (precious metals, Raney nickel, tungsten carbide, molybdenum sulfides, tungsten sulfides, or similar suitable materials) as electrochemically active particles and which may catalyze the cold combustion of fuels such as hydrogen or methanol may be processed.
In generic coating plants, a paste reservoir from which the coating material is supplied to the slot valve and the downstream slot nozzle is usually located upstream of the slot nozzle. Both designs in which the paste reservoir per se is impinged with pressure to press the coating material in the direction of the slot valve as well as designs in which a separate motor-driven conveying means such as a pump, for example, is located between the paste reservoir and the slot valve are conceivable.
A slot valve is understood as a valve in which the supply duct, the nozzle duct, and the valve duct penetrating the valve control rod, in a dimension transverse in relation to the conveying direction, display a considerably larger extent than in the dimension which extends thereto in an orthogonal manner and is likewise transverse in relation to the conveying direction. The extent of the respective ducts in the valve extent direction according to the definition of a slot valve is at least larger by a factor of 4 than the extent transverse to the valve extent direction. With respect to the valve control rod it displays a length in the valve extent direction, along which the valve control rod is penetrated by the valve duct, that is at least four times the mean radius of the valve control rod. Preferably and most commonly, the length of the valve control rod, along which it is penetrated by the valve duct, is larger than the radius of the valve control rod by a greater factor, preferably by at least a factor of 10.
The mentioned correlation between the radius and diameter of the valve control rod, on the one hand, and its length, on the other hand, in practice leads to difficulties. It has emerged, for example, that coating material which makes its way into the narrow gap between the inner circumference of the valve bore and the bearing face of the valve control rod causes the momenta required to readjust the slot valve to surge as the period of operation increases.
This is caused by the tendency of many coating materials and in particular coating materials used in the context of the manufacture of batteries toward significantly increasing their viscosity at a high shear load, depending on the degree and duration of shearing (rheopectic behavior). The longer remnants of the coating material remain between the inner circumferential face of the valve bore and the bearing faces, the greater their viscosity. In practice, the actuators provided on generic slot valves to switch the slot valve can no longer effect a reliable valve switching operation after a certain operating period such that use of the coating plant has to be interrupted and the valve bore has to be cleaned.
It could therefore be helpful to provide a switchable slot valve of the generic type such that the slot valve functions in a maintenance-free manner over a comparatively long period of time.